I personally drink 1 litre of freshly sqeesed apple juice a day for 5 days before the flush - it makes stones softer. but if you have big stones then I suppose you should take GCG.
Yes, Epsom Salt is a magnesium sulfate. I don't think you can get it from chemistry - I bought it from internet - was deliverd next day.
It is not necessary to do parasite cleanse but it is advicable.